Recently, the automobile industry has been aiming to achieve fuel efficiency improvements to meet future legal standards and to reduce the weight of vehicle bodies as a measure to respond to exhaust gas regulations. The body is the heaviest component of the vehicle, accounting for about 40% of the vehicle's total weight.
When the weight of the vehicle body is reduced by about 100 kg, CO2 emission amounts are reduced by 5.0 to 12.5 g. In addition to steel, low-density materials such as aluminum, magnesium and plastic/thermosetting composite materials may be used to reduce the weight of the vehicle body. Accordingly, the diversity and importance of the materials are increasing, and combination with novel materials and adhesion technology and materials that can provide structural merits need to be developed.
Automotive adhesives may be classified into structural adhesives, semi-structural adhesives, non-structural adhesives, double-sided tapes (adhesives), and sealants depending on their strength properties. Examples of the main components of the adhesives/sealants may include PVC, acrylic emulsion, epoxy, urethane, acryl/urethane, and synthetic rubber.
Particularly, urethane-based adhesives are frequently used for automobile interior materials. Reactive hot melts based on urethane chemistry are expensive and poor in terms of safety due to isocyanate included therein. Accordingly, there has been a continuing need for eco-friendly adhesive compositions that can be used in place of urethane-based adhesives.
In order to respond to this need, a variety of polyolefin-based compounds and reactive adhesive compositions including the polyolefin-based compounds may be considered.
U.S. Patent No. 2005/0043455 discloses a crystalline polyolefin homopolymer or copolymer wax which is modified with a silane compound using a free radical reaction and which has a viscosity of 10 to 50,000 mPa·s when measured at 170° C. and a heat of fusion of more than 10 J/g. The silane compound used for the modification includes one or more olefinic double bonds and one or more alkoxy radicals directly attached to the silicon. The polyolefin wax used for the modification is manufactured using a metallocene catalyst. This reference document discloses that a free radical initiator is used in a large amount of 0.1 to 10 wt % based on the polyolefin wax, relative to a silane amount of 0.1 to 40 wt % based on the polyolefin wax.
Further, EP 0944670B1 discloses a crosslinkable elastomer composition that includes a silane-grafted ethylene alpha-olefin interpolymer elastomer having a hardness (Shore A) of 85 or less, and optionally a crystalline olefin polymer. Exposure to water makes it possible to convert the crosslinkable composition into a non-porous, grafted, and crosslinked elastomeric composition having a hardness (Shore A) of 85 or less, and also abrasion resistance greater than that of the crosslinkable composition. This patent discloses that silane is preferably used in an amount of 0.1 to 3.5 wt % and that the ratio of silane to the initiator that is used is relatively high, namely 10:1 to 30:1.
International Publication WO 2005/100501 discloses an article, including 1) a functionalized component, 2) a tackifier, and 3) an olefin polymer, which includes one or more C3 to C40 olefins and optionally one or more diolefins and at most 5 moles of ethylene, and which has a dot T-peel of 1 N or more, a branching index (g′) of 0.95 or less when measured at Mz of a polymer, and a Mw of 100,000 or less. The functional performance is selected from the group consisting of functionalized polymers, functionalized oligomers, and beta nucleation agents. Experimental examples of this reference document relate mainly to a polypropylene-based polymer that is grafted with maleic anhydride.
U.S. Pat. No. 5,824,718 discloses a substantially linear curable ethylene polymer which is useful for wires, cable coatings, weather stripping, and fibers and which is grafted with silane. The silane-grafted polymer may or may not be filled, and cures rapidly compared to many commercial coatings. This patent discloses an ethylene/α-olefin base polymer having a preferable melt index (I2) of 0.5 to 200 g/10 min. See also related patents U.S. Pat. Nos. 5,741,858 and 6,048,935. U.S. Pat. No. 4,806,594 discloses a water-curable composition that includes (a) one or more polymers selected from the group consisting of silane-grafted homopolymers of ethylene, propylene, or 1-butene. In the Example of this patent, polyethylene, having a relatively high molecular weight, is silanized.
U.S. Pat. No. 5,995,474 discloses an adhesive composition including substantially amorphous silane-grafted poly-α-olefin. The adhesive composition is manufactured by grafting a silane compound, having a moiety containing one to three alkoxy groups and one or more olefinic double bonds directly attached to silicon on substantially amorphous poly-α-olefin, and subsequently performing crosslinking using water. This patent relates mainly to a propylene-based polymer.
However, in the case of a known method of silane modification (grafting) where a curable petroleum resin is manufactured to apply to a reactive adhesive, the grafting ratio of the silane compound is low. Accordingly, it insufficiently exhibits a desired curing rate and adhesion strength.